Business Segment Information - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Deposit transactions and cash management	$ 179	$ 171	$ 175
Fixed income	133	205	406
Brokerage, management fees and commissions	90	92	88
Card and digital banking fees	77	84	78
Other service charges and fees	54	54	44
Trust services and investment management	47	48	51
Mortgage banking and title income	23	68	154
Gain on merger termination	225	0	0
Securities gains (losses), net	(4)	18	13
Other income (loss)	103	75	67
Total noninterest income	927	815	1,076
Underwriting, Portfolio Advisory, and Other Noninterest Income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	42	43	44
Regional Banking
Disaggregation of Revenue [Line Items]
Deposit transactions and cash management	161	153	157
Fixed income	0	0	0
Brokerage, management fees and commissions	90	92	88
Card and digital banking fees	68	75	67
Other service charges and fees	30	32	23
Trust services and investment management	47	48	51
Mortgage banking and title income	0	0	0
Gain on merger termination	0
Securities gains (losses), net	0	0	0
Other income (loss)	37	43	52
Total noninterest income	433	443	438
Specialty Banking
Disaggregation of Revenue [Line Items]
Deposit transactions and cash management	10	9	12
Fixed income	133	205	406
Brokerage, management fees and commissions	0	0	0
Card and digital banking fees	2	2	3
Other service charges and fees	24	22	17
Trust services and investment management	0	0	0
Mortgage banking and title income	23	68	152
Gain on merger termination	0
Securities gains (losses), net	0	0	0
Other income (loss)	17	6	7
Total noninterest income	209	312	597
Corporate
Disaggregation of Revenue [Line Items]
Deposit transactions and cash management	8	9	6
Fixed income	0	0	0
Brokerage, management fees and commissions	0	0	0
Card and digital banking fees	7	7	8
Other service charges and fees	0	0	4
Trust services and investment management	0	0	0
Mortgage banking and title income	0	0	2
Gain on merger termination	225
Securities gains (losses), net	(4)	18	13
Other income (loss)	49	26	8
Total noninterest income	$ 285	$ 60	$ 41